CHARACTERIZATION OF GLUTAMINE TRANSPORT IN STREPTOCOCCUS-MUTANS
CHARACTERIZATION OF GLUTAMINE TRANSPORT IN STREPTOCOCCUS-MUTANS
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DOI：
10.1111/j.1399-302x.1995.tb00140.x
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发表时间：
1995-06-01
影响因子：
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通讯作者：
REYNOLDS, EC
中科院分区：
文献类型：
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作者：
DASHPER, SG;RILEY, PF;REYNOLDS, EC
在葡萄糖激活的变形链球菌Ingbritt细胞中谷氨酰胺转运表现出Michaelis-Menten型动力学，V-max为13.4 nmol/mg干重/min，K-t为4.1 μ M。谷氨酰胺扩散到失能的S.变形链球菌表现出相似的动力学类型，K-t为6.8 μ M，但V-max显著降低，为53.9 pmol/mg干重/min。变形杆菌不是质子动力驱动的，因为被激励的细胞的谷氨酰胺的细胞内积累远远超过质子动力的热力学极限，并且在高K+培养基中短杆菌肽对该质子动力的耗散不会降低细胞内谷氨酰胺浓度。因此，谷氨酰胺转运可能是由ATP水解提供能量的。转运蛋白的活性在pH 6.0和7.0之间最大，在pH 7.0以上迅速下降。谷氨酰胺的转运不受天冬酰胺、谷氨酸或天冬氨酸的竞争性抑制，表明存在一个特异的谷氨酰胺转运系统。细胞提取物的反相高压液相色谱显示，进入细胞的大约26%的谷氨酰胺在10分钟内转化为谷氨酸。结果与转运的谷氨酰胺在细胞内谷氨酰胺酶的作用下转化为谷氨酸和氨一致。因此谷氨酰胺可能是细胞氮的重要来源。
Glutamine transport in glucose-energized cells of Streptococcus mutans Ingbritt exhibited Michaelis-Menten-type kinetics with a V-max of 13.4 nmol/mg dry weight/min and a K-t of 4.1 mu M. Diffusion of glutamine into de-energized cells of S. mutans displayed similar type kinetics, with a K-t of 6.8 mu M but with a markedly reduced V-max of 53.9 pmol/mg dry weight/min. Glutamine transport in S. mutans is not proton motive force-driven, as the intracellular accumulation of glutamine by energized cells far exceeded the thermodynamic limits of the proton motive force, and the dissipation of this proton motive force by gramicidin in a high K+ medium did not decrease the intracellular glutamine concentration. Glutamine transport is therefore likely to be energized by ATP hydrolysis. The activity of the transporter was maximal between pH 6.0 and 7.0 and decreased rapidly above pH 7.0. The transport of glutamine was not competitively inhibited by asparagine, glutamate or aspartate, indicating a specific glutamine transport system. Reversed-phase high-pressure liquid chromatography of cell extracts revealed that approximately 26% of the glutamine taken into the cell was converted to glutamate within 10 min. The results are consistent with transported glutamine being converted to glutamate and ammonia by the action of an intracellular glutaminase. Glutamine therefore may be an important source of nitrogen for the cell.